Make link to case study more obvious

Link on the homepage to https://about.gitlab.com/case-studies/360i-transitions-to-gitlab/

Associate Director - 360i => Associate Director - 360i explains in a case study of their transition from SVN

/cc @JobV @Vineste

Status changed to closed by commit bbaf9d1a

Status changed to reopened

@JobV maybe underline the word case study?

Status changed to closed by commit a8942356

updated styles a bit, added underline and hover effect to the case study.

mentioned in commit a8942356

mentioned in commit bbaf9d1a